Braking system architectures for aircraft are known that comprise:                brakes having electromechanical actuators for selectively applying a braking force on respective stacks of disks in order to exert a braking torque on respective wheels;        at least one power module for sending electrical power to the electromechanical actuators in order to enable them to exert a braking force;        at least one control module for controlling the power module in response to braking setpoints so that the appropriate alternative current (AC) power delivered to the actuators enable them to develop the desired braking force: and        at least one power supply unit having means for generating a high voltage from an electrical power bus of the aircraft and/or from a battery of the aircraft in order to supply the power module with the high power needed for powering the actuators.        
In general, the control module and the power module are grouped together in a controller known as an electromechanical actuator controller (EMAC). The EMAC generally incorporates control over a locking member of the electromechanical actuator in order to lock it in position for the purpose of providing a parking brake, which member requires only low voltage for its actuation.
The power supply unit generally comprises one or more converters (e.g. transformers) suitable for transforming the power delivered by the power bus of the aircraft or from its battery into calibrated high voltage power for satisfying the calls for high power generated by the power module of the EMAC.
The commands delivered by the control module to the power module are prepared on the basis of various braking setpoints that come in particular from a braking computer that performs the auto-brake function and that implements anti-slip protection, and also from brake pedals or from a parking brake selector.
The entire braking system of the aircraft is generally designed to operate in three modes: a normal mode; an emergency mode; and a parking brake mode.
In the normal mode, the control module generates a command for the power module as a function of a digital braking setpoint it receives from the braking computer.
In the emergency mode, in which the braking computer has failed, the control module generates a command for the power module as a function of an analog braking setpoint, specifically pedal signals representative of the extent to which the brake pedals have been pressed in as actuated directly by the pilot.
In parking brake mode, which has priority over the other modes, the control module generates a parking brake command in response to a discrete parking brake setpoint issued when the pilot actuates a parking brake selector. In order to enable parking brake to be maintained even when the aircraft is not operating, the actuators are fitted with a fail-safe brake that, when not electrically powered, locks the pusher in position.
A complete braking system for an aircraft having four brake wheels is illustrated for example in document U.S. Pat. No. 6,296,325.
The EMACs are supplied with high power by power supply units delivering high voltage direct current (HVDC) power. The power supply units are preferably fitted with respective power switches that are controlled as a function of the braking setpoints in order to place such a switch in an on state only if braking is actually required, as disclosed in document FR 2 857 642.
In that type of architecture, EMACs receive digital braking setpoints from braking calculators. At least some of the EMACs also receive analog or discrete devices from pedals or from a parking brake selector. The digital setpoint corresponds to normal braking, while the analog or discrete signals make emergency braking or parking brake possible.